#include<iostream>
#include<vector>
using namespace std;

int solution(std::vector<int> cards) {
    // Edit your code here
    int n = cards.size();
    int ret = 0;
    for (int i = 0; i < n; i++)
    {
        ret ^= cards[i];
    }
    return ret;
}

int main()
{
    cout << solution({1,1,2}) << endl;
	return 0;
}